How can I represent an exothermic reaction in a potential energy diagram?

An exothermic reaction is a reaction in which energy is given off, or, in other words, a reaction that has a `DeltaH<0` (see: enthalpy).

Here's a potential energy diagram for an exothermic reaction, the combustion of glucose

![http://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/ch15.html]()

Notice that the potential energy of the reactants (`C_6H_12O_6 + 6O_2`) is smaller than the potential energy of the products (`6CO_2 + 6H_2O`); this difference in potential energy (on this diagram labeled as the energy released by the forward raection or required for the reverse reaction ) represents `DeltaH`.

We know that `DeltaH = H_(f) - H_i`, where

`H_f` represents the enthalpy (potential energy) of the products;
`H_i` represents the enthalpy (potential energy) of the reactans;

Since `H_f` is smaller than `H_i`. `DeltaH` will be smaller than zero (negative), a value that characterizes exothermic reactions.

So, let's say you would have to draw the diagram for the combustion of glucose. You'd start with the balanced chemical equation

`C_6H_12O_6 + 6O_2 -> 6CO_2 + 6H_2O`

Then you'd calculate `H_i` as the sum of the standard state enthalpies (`DeltaH_f^@` - usually given to you) of the reactans - each multiplied by their stoichiometric coefficients, and `H_f` as the sum of the standard state enthalpies of the products - again, each multiplied by their stoichiometric coefficients.

After this point, you'd just graph these values, along with `DeltaH = H_(f) - H_(i) <0` (in this case).